Artificial CO2-infused groundwater injections into a shallow aquifer system have been performed twice since 2014 by K-COSEM research group at a site in Eumseong, Korea, which was specially constructed to study environmental impacts of CO2 leakage on shallow aquifer system. The first injection was performed for 6 hours (short-term injection) as pulse-type leakage of CO2 under a natural hydraulic gradient (0.02) imitating point leaking situation along vertical preferential pathway such as fracture or crack in an injection pipe. In the second injection, CO2 was continuously injected for 30 days (long-term injection) under a forced hydraulic gradient (0.2) considering CO2 leakage events that can be happened in wide-ranging areas. CO2-infused and tracer gases dissolved groundwater were injected below groundwater table through a well, and various monitoring methods were employed not only for saturated but also for unsaturated zones. As parts of this monitoring, hydro-geophysical monitoring has been applied to identify the flow path of injected CO2 and gas tracers and to trace the temporal and spatial distribution of CO2 plume. CO2 concentration is monitored in real time using a non dispersive infra red (NDIR) sensor and an open loop-air purging (OL-AP) system. Temperature and hydraulic parameters (pH and EC) were also collected while, several gas tracers (He, Ar, Kr, SF6), total inorganic carbon (TIC) and carbon isotope (δ13C) were periodically measured. Further, time-lapse (TL) 3D electrical-resistivity (ER) surveys were also performed at before, during and after the injections. Hydro-geophysical monitoring results for the short-term injection showed that injected CO2 migrated along the preferential pathway identified through hydraulic interference tests. On the other hand, TL 3D ER surveys for the long-term injection test showed that CO2 plume migrated along the direction of the ground water flow, while gas tracer data as well as geochemical data such as pH, EC and pCO2 indicated that the migration of CO2 plume was well controlled by the forced hydraulic gradient. The monitoring results indicated that detection of CO2 leakage into groundwater was more effectively performed by using a hydro-geophysical method in order to capture by-passing plume. With this concept, the direct injection of CO2 gas into a shallow aquifer system was proposed. The injection and monitoring tests at the K-COSEM site indicated that CO2 leakage or by-passing CO2 plume in groundwater can be more effectively detected under a monitoring system based on hydro-geophysical method.
Financial support was provided by the “R&D Project on Environmental Management of Geologic CO2 storage” from the KEITI (Project number: 2018001810002) and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2018R1C1B6007390).